Crystal structures of (azido)(pentamethylcyclopentadienyl)iridium(III) complexes containing various types of bidentate ligands

Article abstract of DOI:10.1016/j.poly.2009.04.010

Several (azido)iridium(III) complexes having a pentamethylcyclopentadienyl (Cp*) group, [Cp*Ir(N₃)₂(Ph₂Ppy-κP)] (1: Ph₂Ppy = 2-diphenylphosphinopyridine), [Cp*Ir(N₃)(Ph₂Ppy-κP,κN)]CF_3<

Full text of DOI:10.1016/j.poly.2009.04.010

Polyhedron 28 (2009) 2287–2293
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Crystal structures of (azido)(pentamethylcyclopentadienyl)iridium(III)
complexes containing various types of bidentate ligands
b
a
a
Takayoshi Suzuki a,b, , Mai Kotera , Asuka Takayama , Masaaki Kojima
*
a Department of Chemistry, Faculty of Science, Okayama University, Okayama 700-8530, Japan
b Department of Chemistry, Graduate School of Science, Osaka University, Toyonaka 560-0043, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
*
*
Several (azido)iridium(III) complexes having a pentamethylcyclopentadienyl (Cp ) group, [Cp Ir(N3)2-
(Ph2Ppy-
Received 16 January 2009
Accepted 14 April 2009
Available online 21 April 2009
* *
jP)] (1: Ph2Ppy = 2-diphenylphosphinopyridine), [Cp Ir(N3)(Ph2Ppy-jP,jN)]CF3SO3 (2), [Cp -
Ir(N3)(dmpm)]PF6
(3:
dmpm = bis(dimethylphosphino)methane),
[Cp*Ir(N3)(Ph2Pqn)]PF6ꢀCH3OH
*
(4ꢀCH3OH: Ph2Pqn = 8-diphenylphosphinoquinoline), and [Cp Ir(N3)(pybim)] (5: Hpybim = 2-(2-pyri-
dyl)benzimidazole) have been prepared and their crystal structures have been analyzed by X-ray diffrac-
Keywords:
Iridium(III) azido complexes
Crystal structures
8-Quinolylphosphine
2-Pyridylphosphine
2-(2-Pyridyl)benzimidazolate
tion. In complex 1, the Ph2Ppy ligand is only coordinated via the P atom (-
bidentate ligand through the P and N atoms (- P, N) to form a four-membered chelate ring. Comparing
the structural parameters of the chelate ring in 2 with those of a similar five-membered chelate ring
formed by Ph2Pqn in 4, it became apparent that the angular distortion in the Ph2Ppy- P, N ring was
remarkable, although the Ir–P and Ir–N bonds in the Ph2Ppy- P, N ring were not elongated very much
from the corresponding bonds in the Ph2Pqn- P, N ring. In the pybim complex 5, the five-membered
jP), while in 2 it acts as a
j
j
j
j
j
j
j
j
chelate ring was coplanar with the pyridine and benzimidazolyl rings. With the related (azido)iridium(III)
complexes analyzed previously, comparison of the structural parameters of the Ir–N3 moiety in [Cp*
IrIII(N3)(L–L0)]+/0 complexes reveals an anomalous feature of the 2,20-bipyridyl (bpy) complex,
*
[Cp Ir(N3)(bpy)]PF6.
Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction
This interesting reaction seems to be attributable to the highly
strained chelate ring and the stability of the Ir–S bond of the above
Recently, the investigation of transition-metal azido complexes
has been revived because they often show interesting chemical
reactivities and physical properties [1–4]. For example, photolysis
of some azido complexes results in higher-valent metal nitrido
complexes, which have the potential for further nitrogen-atom
(or imino-group) transfer reactions [2]. The crick reactions of azido
complexes with nitriles or alkynes via 1,3-dipolar cycloaddition,
which affords the corresponding tetrazolato or triazolato com-
plexes, are also attractive for the creation of new functional com-
pounds [3]. Furthermore, the azido-bridged dinuclear complexes
or cluster compounds are of current interest in studies of supramo-
lecular architecture and the development of molecular magnetic
dithiocarbamato or thiolato ligands. On the other hand, it is also
III
*
known that some Cp Ir complexes having phosphines or imida-
zolates often exhibit interesting structural features and novel
III
*
reactivities [8–11]. Therefore, the related Cp Ir (N3) complexes
bearing 2-diphenylphosphinopyridine (Ph2Ppy), 8-diphenylphos-
phinoquinoline (Ph2Pqn), bis(diphenyl- or dimethylphosphi-
no)methane (ꢁdppm or dmpm), as well as 2-(2-pyridyl)benzimidaz-
olate (pybim ) (L–L0: Scheme 2) may be possible candidates for
similar or other fascinating reactions. Here, we have prepared such
III
complexes of [Cp Ir (N3)(L–L )]+/0, and their molecular structures
0
*
and chemical reactivities were compared, together with the analo-
gous complexes characterized previously in our group [5,7,12,13].
materials [4]. We have also investigated the photochemical reac-
III
*
tivities of (azido)iridium(III) complexes with
(Cp* =
tion reaction on photolysis of [Cp Ir(N3)(R2dtc, 2-Spy, or 2-Sqn)]
a
Cp Ir (N3)
2. Experimental
g
5-C5Me5) fragment, and found a novel nitrogen-atom inser-
*
(R2dtcꢁ = N,N-dialkyldithiocarbamate;
2-Spyꢁ = 2-pyridinethio-
2.1. Preparation of complexes
late; 2-Sqnꢁ = 2-quinolinethiolate) complexes (Scheme 1) [5–7].
The diazidoiridium(III) complex, [Cp*Ir(N3)2]2 [12], and the
phosphines, Ph2Ppy [14] and Ph2Pqn [15], were prepared by the
literature methods. The ligands, dmpm and 2-(pyridyl)benzimid-
azole (Hpybim), were purchased from Aldrich Co. Ltd.
* Corresponding author. Address: Department of Chemistry, Faculty of Science,
Okayama University, Okayama 700-8530, Japan. Tel./fax: +81 86 251 7900.
E-mail address: suzuki@cc.okayama-u.ac.jp (T. Suzuki).
0277-5387/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2009.04.010

2288
T. Suzuki et al. / Polyhedron 28 (2009) 2287–2293
The corresponding PF6 salt (20) was prepared similarly using
AgPF6, instead of Ag(O3SCF3).
N
N
N
Ir
N
S
S
hν
2.1.3. [Cp*Ir(N3)(dmpm)]PF6 (3)
S
N
Ir
The ligand, dmpm (26 mg, 1.9 mmol) was added dropwise by
syringe to a red suspension of [Cp*Ir(N3)2]2 (400 mg, 0.972 mmol)
in methanol (10 cm3) under a dinitrogen atmosphere. The reaction
mixture was stirred at room temperature for 30 min and evapo-
rated to dryness under reduced pressure. The residue was washed
with Et2O (10 cm3 ꢂ 3), and then dissolved in methanol (2 cm3)
under air. A saturated methanol solution containing NH4PF6
(800 mg, 4.9 mmol) was added to the filtered methanol solution.
The mixture was allowed to stand for 30 min to afford a pale yel-
low precipitate, which was collected by filtration, washed with
methanol (1 cm3) and Et2O (3 cm3), and dried in vacuo. The crude
product was dissolved in a mixture of acetonitrile and methanol
(1:1), and Et2O vapor was diffused into the filtered solution to give
yellow crystals of 3. Yield: 432 mg (69%). Anal. Calc. for
C15H29F6IrN3P3: C, 27.69, H, 4.49; N, 6.46%. Found: C, 27.93; H,
CH3CN
S
N
N
N
N
N
S
hν
N
N
Ir
Ir
CH3CN
S
Scheme 1.
4.47; N. 6.33%. 1H NMR (CD3CN, 303 K):
1JHP + 3JHP = 6.6 Hz, PMe, 6H), 1.83 (virtual t, JHP + 3JHP = 6.2 Hz,
d 1.66 (virtual t,
PPh2
N
Me2P
PMe2
1
Ph2Ppy
dmpm
*
PMe, 6H), 1.93 (s, Cp , 15H), 3.49 (q, JHP and JHH = 15.9 Hz, CH2,
1H), 4.68 (dt, JHP = 15.6, JHH = 10.5 Hz, CH2, 1H).
N
2.1.4. [Cp*Ir(N3)(Ph2Pqn)]PF6 (4)
Ph2Pqn (74.8 mg, 0.239 mmol) was added to a suspension of
[Cp*Ir(N3)2]2 (96.5 mg, 0.117 mmol) in methanol (5 cm3), and the
mixture was stirred at room temperature for 8 h. A methanol solu-
tion (3 cm3) of NH4PF6 (137 mg, 0.839 mmol) was added to the
resulting orange solution, affording an immediate precipitation.
The precipitate was filtered off, washed with methanol (2 cm3),
and dried in vacuo. The crude product was recrystallized from ace-
tonitrile/methanol to form orange platelet crystals. Yield: 171 mg
(88%). Anal. Calc. for C31H31F6IrN4P2: C, 44.98; H, 3.77; N, 6.77%.
Found: C, 44.68; H, 3.93; N, 6.95%. 1H NMR (CD3CN, 303 K) d 1.56
N
N
PPh2
N
pybim–
Ph2Pqn
Scheme 2.
Caution! The AgN3 resulting from the preparation of complex 2
is potentially explosive. Although we had no severe experience in
our laboratory, all experiments handling the precipitated AgN3
should be performed with the greatest care.
*
(d, JHP = 2.4 Hz, Cp ).
2.1.1. [Cp*Ir(N3)2(Ph2Ppy-jP)] (1)
A methanol solution (6 cm3) of Ph2Ppy (135 mg, 0.57 mmol)
was added with stirring to a solution of [Cp*Ir(N3)2]2 (236 mg,
0.287 mmol) in a mixture of dichloromethane and methanol (1:1,
4 cm3), affording a yellow–brown precipitate in a few minutes.
The reaction mixture was concentrated (to ca. 5 cm3) under re-
duced pressure, and the resulting precipitate was collected by fil-
tration. The crude product was washed with methanol (1 cm3)
and diethyl ether (3 cm3), and recrystallized from a mixture of
dichloromethane and methanol to give orange platelet crystals.
Yield: 244 mg (63%). Anal. Calc. for C27H29IrN7P: C, 48.06; H,
4.33; N, 14.53%. Found: C, 47.91; H, 4.28; N, 14.41%. 1H NMR
2.1.5. [Cp Ir(pybim)(N3)] (5)
*
A methanol solution (3 cm3) of Hpybim (46.7 mg, 0.239 mmol)
and NaOCH3 (13.8 mg, 0.255 mmol) was added to a suspension of
[Cp*Ir(N3)2]2 (103.5 mg, 0.126 mmol) in a mixture of dichloro-
methane and methanol (2:1, 3 cm3). The mixture was stirred at
room temperature for 8 h and concentrated to ca. 1 cm3 by a flow
of dinitrogen. The resulting yellow precipitate was collected by fil-
tration and dried in vacuo. Yield: 109.4 mg (77%). Anal. Calc. for
C22H23IrN6: C, 46.88; H, 4.11; N, 14.91%. Found: C, 46.50; H, 4.21;
N, 14.88%. Yellowish orange platelet crystals suitable for the X-
ray diffraction study were obtained from a mixture of dichloro-
methane and methanol.
*
(CD2Cl2, 303 K): d 1.44 (d, JHP = 2.4 Hz, Cp , 15H), 7.10–7.57 (m,
Ph and py, 13H), 8.70 (dq, JHH = 31.9 and 0.9 Hz, 6-py, 1H).
2.2. Measurements
2.1.2. [Cp*Ir(N3)(Ph2Ppy-jP,jN)]O3SCF3 (2)
A methanol solution (3 cm3) of Ag(O3SCF3) (97 mg, 0.38 mmol)
was added dropwise with stirring to an orange solution of 1
(255 mg, 0.378 mmol) in dichloromethane (2 cm3). The mixture
was stirred in the dark at room temperature for 18 h, and the
resulting white precipitate (AgN3) was filtered off. The precipitate
was washed successively with acetonitrile (5 cm3), methanol
(5 cm3) and dichloromethane (5 cm3), and the filtrate and all wash-
ings were combined. The mixture was evaporated to dryness under
reduced pressure, and the orange residue was dissolved in hot
methanol (50 °C, 3 cm3). After removal of undissolved impurities
by filtration, the filtrate was allowed to stand in a refrigerator over-
night, affording yellow–brown prismatic crystals. Yield: 226 mg
(76%). Anal. Calc. for C28H29F3IrN4O3PS: C, 43.02; H, 3.74; N,
7.17%. Found: C, 43.09; H, 3.79; N, 7.14%.
Proton NMR spectra were acquired on a JEOL EX270 or a Varian
Mercury 300 spectrometer; chemical shifts were referenced to the
residual 1H NMR signals of the deuterated solvent and are reported
versus TMS. Infrared spectra were measured on a JASCO FT/IR FT-
550 spectrophotometer using Nujol mulls.
2.3. Crystallography
The X-ray diffraction data were obtained at ꢁ73(2) °C on a
Rigaku R-axis rapid imaging plate detector with a graphite-mono-
chromated Mo Ka radiation (k = 0.71073 Å). A suitable crystal was
mounted with a cryoloop and flash-cooled by cold dinitrogen
stream. Data were processed by the Process-Auto program package
[16a], and absorption corrections were made by the numerical

T. Suzuki et al. / Polyhedron 28 (2009) 2287–2293
2289
Table 1
Crystal data of complexes.
Compound
1
2
3
4ꢀCH3OH
5
Formula
FW
C27H29IrN7P
674.74
C28H29F3IrN4O3PS
781.78
C15H29F6IrN3P3
650.52
C32H35F6IrN4OP2
859.78
C22H23IrN6
563.66
T/(K)
200(2)
200(2)
200(2)
200(2)
200(2)
Crystal system
Space group, Z
a/(Å)
b/(Å)
c/(Å)
monoclinic
P21/a, 4
17.5522(7)
8.6997(4)
17.5992(8)
99.063(1)
2653.8(2)
1.689
monoclinic
P21/a, 4
monoclinic
P21/c, 4
monoclinic
P21/c, 4
monoclinic
P21/n, 4
8.2833(5)
16.2409(10)
14.4564(9)
98.113(2)
1925.3(2)
1.945
10.0102(5)
28.3235(12)
10.5269(5)
96.222(2)
2967.0(2)
1.750
8.7472(9)
16.771(2)
15.705(2)
91.949(3)
2302.7(5)
1.876
8.6711(4)
14.3015(6)
26.485(1)
93.975(1)
1843.3(13)
1.743
b/(°)
V/(Å3)
Dx/(Mg mꢁ3
)
l(Mo K
a
)/(mmꢁ1
)
5.135
4.680
6.061
4.240
6.957
Tmin, Tmax
Rint
0.427, 0.628
0.033
0.455, 0.604
0.030
0.377, 0.582
0.065
0.417, 0.484
0.048
0.337, 0.543
0.042
Reflection/parameter ratio
6056/331
0.019
4196/227
0.019
5182/263
0.068
7475/416
0.033
4398/268
0.025
2
R1 [Fo > 2
r
(Fo2)]
wR2 (all reflection)
0.042
0.082
0.228
0.082
0.058
Goodness of fit
1.046
1.183
1.177
1.080
1.125
*
method from the crystal shapes [16b]. The structures were solved
by the direct method using SIR2004 [17a], and refined on F2 (with
all independent reflections) using SHELXL97 [17b]. All non-H atoms
were refined anisotropically, and H atoms were introduced at the
positions calculated theoretically and treated with riding models.
for [Cp Ir(N3)2(napy-
j
N)] (napy = 1,8-naphthyridine) [12],
a
stoichiometric reaction of [Cp*Ir(N3)2]2 and Ph2Ppy (1:2 mole ratio)
in a mixture of dichloromethane and methanol afforded an orange
crystalline product of [Cp*Ir(N3)2(Ph2Ppy)] (1) in 63% yield.
The molecular structure of 1 determined by single-crystal X-ray
analysis is illustrated in Fig. 1, which revealed the monodentate
coordination mode of Ph2Ppy through the P atom. In this analysis,
three six-membered rings bound to the P atom, i.e., two phenyl and
one pyridyl rings, were not distinguishable from one another, and
the N atom of Ph2Ppy could not be specified [19,20]. We tentatively
assigned the N atom to the atom that was closest to Ir among the
six possible atoms. Even under this assumption, the Ir1ꢀꢀꢀN1 dis-
tance was 3.537(2) Å, which is far from being a bonding interac-
tion. The structure of the ‘‘Cp*Ir(Ph2Ppy)” moiety in 1 is very
ꢁ
For the compound 3, the positions of the F atoms of PF6 were se-
verely disordered but no satisfactory model could be found. There-
fore, the reported result was an artificially distorted structure for
this anion. All calculations were carried out using the CRYSTAL STRUC-
TURE software package [16c].
Crystal data are collected in Table 1.
3. Results and discussion
*
similar to that in [Cp IrCl2(Ph2Ppy-
jP)] [18]; the Ir–P bond lengths
3.1. 2-Diphenylphosphinopyridine (Ph2Ppy) complexes
in 1 (2.3060(6) Å) and in the dichloro complex (2.299(2) Å) are
*
comparable. Also, the ‘‘Cp Ir(N3)2” moiety corresponds well to that
Kollipara et al. have recently reported the syntheses of
[Cp*IrCl2(Ph2Ppy)], [Cp*IrCl(Ph2Ppy)2]PF6 and [Cp*IrCl(Ph2Ppy)]PF6,
as well as the crystal structures of the first two complexes having
monodentately P-coordinated ligands (Ph2Ppy-jP) [18]. Similar to
their synthetic procedure and to the preparative method
in [Cp*Ir(N3)2(napy- N)] [9]. The Ir–N(N3) bonds in 1, 2.112(3) and
2.129(2) Å, are comparable to those of the napy complex, 2.114(7)
and 2.126(7) Å. The bending coordination mode and the intrali-
gand structural parameters of the coordinated N3 ligands are also
j
ꢁ
quite similar to those of the napy complex (see: Table 2).
The ligand, Ph2Ppy, has the potential to form a four-membered
chelate ring [21]. However, unlike the related bis(phosphino)meth-
anes (dmpm or dppm; vide infra) and thiolates (2-Spyꢁ or 2-Sqnꢁ),
a simple reaction of Ph2Ppy with [Cp*Ir(N3)2]2 in a mixture of
dichloromethane and methanol did not give the chelate complex.
Kollipara et al. reported the formation of a chelate complex by
the reaction of Ph2Ppy and [Cp*IrCl2]2 in methanol [18]. Here, to
obtain a pure sample in high yield, we have utilized the reaction
of complex 1 with a stoichiometric amount of Ag(O3SCF3) or AgPF6
for the preparation of [Cp Ir(N3)(Ph2Ppy)](O3SCF3 or PF6) (2 or 20).
The chelate coordination mode of Ph2Ppy- P, N was confirmed by
*
j
j
X-ray analysis (Fig. 2). The Ir1–P1 bond length in 2 (2.3159(9) Å) is
nearly the same as that in 1 (monodentately P-coordinated Ph2Ppy
complex). The Ir1–N1 bond length and the chelate bite angle of P1–
Ir1–N1 in 2 are 2.125(3) Å and 67.40(8)°, respectively. These values
are comparable to those in the corresponding 2-Spy complex (Ir–
N = 2.111(4) Å, S–Ir–N = 67.0(1)°) [22] and 2-Sqn complex (Ir–
N = 2.131(5) Å, S–Ir–N = 66.6(2)°) [7]. We expected, therefore, that
the chelate Ph2Ppy complex 2 would be stable, similar to the 2-Spy
and 2-Sqn complexes. However, it was found that complex 2 was
labile in acetonitrile solution.
Fig. 3 depicts the variable-temperature (ꢁ20–40 °C) 1H NMR
Fig. 1. An ORTEP view (50% probability level, hydrogen atoms omitted) of
[Cp Ir(N3)2(Ph2Ppy-
jP)] (1).
spectra of [Cp*Ir(N3)(Ph2Ppy)]PF6 (20) in acetonitrile-d3 (ca.
*

2290
T. Suzuki et al. / Polyhedron 28 (2009) 2287–2293
Table 2
Comparison of the structural parameters (Å, °) of the Cp*IrIII(N3) moiety and the vibration frequency,
m
(N3) (cmꢁ1).
Complex
1
Ir–C
Ir–N
Ir–N –Nb
N –Nb
N –Nb–N
Nb–N
c
m(N3)
a
a
a
a
c
2.180(2)–2.223(2)
2.112(2)
2.129(2)
2.108(3)
2.113(13)
2.122(3)
2.115(3)
2.114(7)
2.126(7)
2.230(6)
2.120(6)
2.132(6)
2.091(6)
2.136(3)
2.109(4)
2.134(4)
118.7(2)
117.4(2)
121.6(2)
117.9(10)
120.5(3)
124.3(3)
124.5(6)
120.5(4)
116.4(6)
122.5(5)
127.3(4)
124.2(5)
120.5(3)
122.4(4)
118.1(4)
1.201(3)
1.198(3)
1.202(4)
1.230(17)
1.195(5)
1.188(5)
1.193(10)
1.180(10)
1.025(12)
1.197(8)
1.178(7)
1.205(8)
1.200(5)
1.181(6)
1.199(6)
176.7(3)
175.0(3)
176.3(4)
1.149(4)
1.153(3)
1.151(5)
1.155(18)
1.151(6)
1.155(5)
1.140(10)
1.170(10)
1.282(15)
1.157(9)
1.127(7)
1.169(8)
1.153(5)
1.158(7)
1.155(6)
2025
2
3
2.171(3)–2.210(3)
2.170(12)–2.285(10)
2.168(4)–2.244(4)
2.152(4)–2.186(3)
2.146(9)–2.185(8)
2036
2035
2035
2034
2034
177.6(18)
175.8(5)
174.4(4)
176.4(9)
176.4(10)
172.3(10)
176.3(8)
175.4(7)
175.3(7)
175.9(5)
175.7(7)
176.3(6)
4ꢀCH3OH
5
[Cp*Ir(N3)2(napy)]
*
[Cp Ir(N3)(bpy)]PF6
2.145(7)–2.179(7)
2.159(7)–2.179(5)
2.144(6)–2.172(5)
2.156(6)–2.174(6)
2.160(4)–2.197(4)
2.155(5)–2.198(5)
2.162(7)–2.202(7)
2022
2030
2035
*
[Cp Ir(Me2dtc)(N3)]
*
[Cp Ir(2-Sqn)(N3)]
[Cp*Ir(8-Sqn)(N3)]
[{Cp*Ir(N3)}2(
2029
l-Hbimt)2]
2036
2042sh
sh: Shoulder
0.05 mol dmꢁ3, prepared under a dinitrogen atmosphere). At 40 °C
the Cp* resonance was observed as a broad signal around d 1.6. On
cooling, this signal separated into two broad resonances with dif-
ferent intensities. At ꢁ20 °C both resonances were detected as
sharp doublets at d 1.51 and 1.64, with an intensity ratio of 4:1.
The doublet resonances are indicative of the existence of an Ir–P
bond, and, therefore, the two species in solution are assumed to
be the chelate and the monodentately P-coordinated Ph2Ppy com-
plexes (Scheme 3). This results indicate that complex 20 exists as an
equilibrium mixture because of the dissociation of the Ir–N(py)
bond in acetonitrile-d3. Such a dissociation would be favorable
[Cp Ir(N3)(2-Spy or 2-Sqn)], while the solution behavior, i.e., the
lability of the Ir–N(py) bond, was obviously different. To elucidate
the reason for the different behavior from the structural point of
view, we have also analyzed the crystal structures of the related
complexes bearing dmpm and Ph2Pqn.
*
3.2. Bis(dimethylphosphino)methane (dmpm) complex
It has been reported that particular PtII–dppm complexes of the
form [Pt(CH2X)2(dppm-j
2P, P)] (X = Cl, Br, or I) demonstrated a fas-
cinating chelate-ring expansion reaction by insertion of a CH2
for
a N-atom insertion reaction, because the reaction of
[Cp*Ir(N3)(2-Spy)] was initiated by the photochemical cleavage of
the Ir–N(py) bond [6]. However, photochemical or thermal reac-
tion of an acetonitrile-d3 solution of complex 20 gave a complicated
mixture of unidentified products, in which there was no lower-
field shifted 1H NMR resonance diagnostic for the two-legged piano
III
0
*
stool structure of Cp Ir (L–L )-type complexes [5–7]. It has also
been reported [23] that photolysis of [Cp*Ir(N3)2(PPh3)] gave
I
*
*
[Cp Ir(H)(Ph2PC6H4-
jP,j
C)], presumably via a ‘‘Cp Ir (PPh3)” tran-
sient species formed by homoleptic cleavage of two Ir–N(N3)
bonds. Thus, the present reactions might be caused by the undesir-
able thermal or photoreduction of the iridium(III) azido complex.
As mentioned above, the Ir–N(py) bond length and the chelate
bite angle of complex
2 were comparable to those of
Fig. 3. Variable-temperature 1H NMR spectra in the Cp* region of
[Cp*Ir(N3)(Ph2Ppy-
j
P,
j
N)]PF6 (20) in CD3CN.
+
CD3
+
C
N
N
N
P
Ir
Ir
P
Ph
CD3CN
Ph
N3
N3
Ph
Ph
Fig. 2. An ORTEP view (50% probability level, hydrogen atoms omitted) of the
*
cation in [Cp Ir(N3)(Ph2Ppy-
jP,
jN)]O3SCF3 (2).
Scheme 3.

T. Suzuki et al. / Polyhedron 28 (2009) 2287–2293
2291
Fig. 4. An ORTEP view (50% probability level) of the cation in [Cp*Ir(N3)(dmpm)]PF6
(3).
Fig. 5. An ORTEP view (50% probability level, hydrogen atoms omitted) of the
cation in [Cp*Ir(N3)(Ph2Pqn)]PF6ꢀCH3OH (4ꢀCH3OH).
group into a Pt–P bond [24], which is somewhat related to a
N-atom insertion reaction. Thus, we thought it might be interesting
to investigate the structures and reactivities of the bis(phos-
phino)methane complexes of [Cp*Ir(N3)(P–P)]PF6 (P–P = dppm or
dmpm). These complexes were prepared in good yields by reaction
of [Cp*Ir(N3)2]2 and the phosphines in methanol, followed by isola-
tion of the PF6 salts on addition of NH4PF6. We have also prepared
the CF3SO3, BF4 and BPh4 salts of the dppm complexes, but none of
them deposited suitable crystals for an X-ray diffraction study.
Instead, we have determined the crystal structure of
[Cp*Ir(N3)(dmpm)]PF6 (3). The molecular structure with a four-
membered chelate ring was confirmed, as illustrated in Fig. 4.
The chelate bite angle, P1–Ir1–P2, of dmpm in complex 3 is
71.0(1)°, which is larger than those of Ph2Ppy in complex 2,
67.40(8)°. The Ir1–P1–C3 and Ir1–P2–C3 angles in 3 are 93.3(5)
and 95.7(4)°, respectively, which are larger than the Ir1–P1–C2 an-
gle in 2, 85.9(1)°. These angular differences indicate clearly that the
steric strain effects are more severe in the Ph2Ppy chelate than in
the dmpm chelate. It is also notable that two Ir–P bonds of complex
3 showed a large numerical deviation, Ir1–P1 2.344(4) versus Ir1–
P2 2.282(3) Å, but we cannot account for this unusual feature at
present.
Unlike the Ph2Ppy chelate in complex 2, the four-membered
chelate rings in the dppm and dmpm complexes were stable in
acetonitrile solution. When acetonitrile-d3 solutions of the dppm
and dmpm complexes were photolyzed by a high-pressure Hg
lamp under a dinitrogen atmosphere at temperature below 0 °C,
the 1H NMR spectra of the resulting solutions indicated the forma-
tion of a complicated mixture of unidentified products. Similar to
the case of Ph2Ppy complex 2, there was no lower-field shifted res-
onance diagnostic for Cp*IrIII complexes with a two legged piano
titative yield, and deposited orange prismatic crystals with a meth-
anol molecule of crystallization, 4ꢀCH3OH. The molecular structure
of the cation in 4ꢀCH3OH revealed by the X-ray diffraction study is
shown in Fig. 5.
The chelate bite angle of Ph2Pqn (P1–Ir1–N1) in complex 4 is
81.25(9)°, which is comparable to those in the other Ph2Pqn com-
plexes determined previously [21,25], but much larger than that of
Ph2Ppy in complex 2, 67.40(8)°. The five-membered chelate ring is
almost planar, and coplanar with the quinolyl ring. The deviations
of atoms Ir1 and P1 from the least-square quinolyl ring plane are
only 0.246(4) and 0.177(4) Å, respectively. The Ir1–P1–C8 angle
in the chelate ring is 102.2(1)°, which is a little smaller than the
ideal tetrahedral angle, but is normal for the coordinated phos-
phines. All bond angles around N1 are nearly 120°. These values
indicate that the chelate coordination of Ph2Pqn forms a strain-free
planar five-membered ring. The Ir1–P1 and Ir1–N1 bond lengths in
4 are 2.294(1) and 2.115(3) Å, respectively, which are comparable
*
*
to those in [Cp Ir(8-Sqn)(N3)] (Ir–N 2.104(3) Å), [Cp IrCl(8-MeS-
qn)]PF6 (Ir–N 2.094(3) Å) [26], and the Ph2Ppy complex 2 (vide su-
pra). It is surprising that the Ir–P and Ir–N bonds in the highly
strained four-membered Ph2Ppy chelate ring elongate only by
0.02 and 0.01 Å, respectively, while the bond angles in the Ph2Ppy
ring show severe deviation from the ideal values: P–Ir–N 67.40(8)°,
Ir–P–C 85.4(1)°, and Ir–N–C 106.3(2)°. This observation suggests
that the primary reason for the dissociation of the Ir–N(py) bond
of the Ph2Ppy complex 2 in solution must be an angular strain in
the four-membered chelate ring. In other words, even the bond
lengths are seemingly comparable, the coordination bond in the
strained chelate ring is remarkably weak and easy to dissociate
in solution to relieve the steric strain.
In the crystal structure of 4ꢀCH3OH, there was a stacking inter-
action between the quinolyl rings with a neighboring molecule,
forming a dimer unit. The distance between the planes is ꢃ3.6 Å.
This stacking interaction is the most remarkable difference from
the crystal structure of the Ph2Ppy complex 2.
*
stool structure. However, most of the Cp resonances became dou-
blets (cf. the reactant complexes showed a triplet), because of cou-
pling to the single P nucleus. This may suggest that a N-atom
insertion could have taken place on photolysis.
3.3. 8-Diphenylphosphinoquinoline (Ph2Pqn) complex
3.4. 2-(2-Pyridyl)benzimidazolato (pybim) complex
To clarify the structural features of the Ph2Ppy chelate ring in
complex 2, the corresponding Ph2Pqn complex was prepared and
characterized by X-ray diffraction analysis for comparison. The
In a series of studies we are investigating the molecular struc-
tures and photochemical reactivities of (azido)iridium(III) com-
plexes containing various kinds of bidentate coligands,
[Cp*IrIII(N3)(L–L0)]+/0. Previously, we have reported the crystal
*
complex, [Cp Ir(N3)(Ph2Pqn)]PF6 (4), was obtained in nearly quan-

2292
T. Suzuki et al. / Polyhedron 28 (2009) 2287–2293
*
comparable to that of bpy in [Cp Ir(N3)(bpy)]PF6, 76.8(2)° [13].
The Ir1–N2(py) bond length in 5, 2.139(3) Å, is longer than the
Ir–N(bpy) bonds in the above bpy complex, 2.086(5) and
2.097(5) Å. The Ir–N1(bim) bond in 5 is 2.087(3) Å, which is
remarkably shorter than the Ir1–N2(py) bond and comparable to
the Ir–N(bim) bond length in a dinuclear 2-benzimidazolethiolato
ꢁ
*
(Hbimt ) complex of [{Cp Ir(N3)}2(
l
-Hbimt)2]ꢀCH3OH, 2.098(4) Å
[7]. Because the N ligator in the anionic benzimizadolate ring is
more basic than that in the neutral pyridine ring, the bim-N donor
would give a stronger
r
-bonding interaction with an IrIII center
than the py-N does. When the bite angle of the ligands, N–E, are
compared in [Cp*IrIII(N3)(N–E)]0/+ having a planar five-membered
chelate ring, the angle increases in the order (N–E =) pybimꢁ ꢄ
bpy < Ph2Pqn < 8-Sqnꢁ. The same order was observed in the Ir–E
bond lengths: Ir–N(pybim) 2.087(3) ꢄ Ir–N(bpy) 2.092(7) < Ir–
P(Ph2Pqn) 2.294(1) < Ir–S (8-Sqn) 2.366(1) Å.
The crystal structure of 5 exhibited a characteristic packing
diagram. As seen in Fig. 7, a planar pybim ring is stacked with
the other pybim ring in a neighboring molecule and a Cp* ring in
another molecule. The interplanar distances between the planes
are ꢃ3.4 Å. In the crystal structure of [Cp*IrCl(Hpyim)]PF6
(Hpyim = 2-(2-pyridyl)imidazole) [9], a similar stacking interac-
tion between a pair of Hpyim ligand planes was observed, in addi-
tion to the hydrogen-bonding interaction between the im-H group
and the coordinated Clꢁ ligand. However, in the present complex 5
the N3 atom of the pybim ligand was free from coordination or
hydrogen-bonding interaction.
Fig. 6. An ORTEP view (50% probability level, hydrogen atoms omitted) of
*
[Cp Ir(N3)2(pybim)] (5).
structure of [Cp*Ir(N3)(bpy)]PF6 [13], which showed an interesting
1,3-dipolar cycloaddition reaction in acetonitrile to form 5-methyl-
tetrazolato complexes [20]. Furthermore, it has also been revealed
that 2-pyridyl and 2-benzimidazolyl groups exhibited a different
coordination behavior, at least when they were incorporated into
bidentate thiolato ligands, i.e., 2-pyridinethiolate (2-Spyꢁ) and
benzimidazole-2-thiolate (Hbimtꢁ) [7]. Thus, to compare directly
the molecular structures between the bpy and pybimꢁ complexes,
we have prepared and characterized the pybim complex,
[Cp*Ir(N3)(pybim)] (5).
3.5. Comparison of the structural parameters of the Cp*IrIII(N3) moiety
The structural parameters of the Cp*IrIII(N3) moiety in the com-
plexes determined in the previous and present studies are col-
lected in Table 2. The Ir–C bond lengths of the complexes
analyzed previously were in the range of 2.14–2.20 Å. However,
some of the Ir–C bonds in complexes 1–4 are slightly longer than
2.20 Å (up to 2.29 Å). A detailed examination revealed that the
elongated Ir–C bonds are all trans to the phosphino donor group(s).
*
Thus, it is concluded that the Ir–C bonds of the Cp group are also
*
Complex 5 was obtained from [Cp Ir(N3)2]2 and Na(pybim) as
affected by the strong trans influence of the phosphines.
The parameters associated with the Ir–N3 moiety are very sim-
ilar among the complexes listed in Table 2, except for the bpy com-
yellow–orange crystals in 77% yield. The molecular structure
determined by X-ray analysis is shown in Fig. 6. As expected, the
anionic pybimꢁ ligand formed a planar five-membered chelate
ring, which is coplanar with the pyridine and benzimidazolate
rings. The chelate bite angle (N1–Ir1–N11) is 76.5(2)°, which is
*
plex of [Cp Ir(N3)(bpy)]PF6. Namely, in most (azido)iridium(III)
complexes the Ir–N bond lengths are in the range 2.09–2.14 Å
a
and the Ir–N –Nb bond angles are in the range 117–127°. The coor-
a
dinated azido ligands are nearly linear (N –Nb–N 174–177°), with
a
c
longer N –Nb (1.18–1.23 Å) bonds than Nb–N (1.13–1.17 Å)
a
c
bonds. In contrast, in [Cp*Ir(N3)(bpy)]PF6 all of the parameters
for the Ir–N3 moiety are outside the above ranges. In particular,
the Ir–N bond is strikingly long at 2.230(6) Å, and the N –Nb bond
a
a
(1.025(12) Å) is remarkably shorter than the Nb–N bond
c
(1.282(15) Å). Consistent with the differences in these structural
parameters, the m(N3) stretching frequency of the bpy complex,
2022 cmꢁ1, is observed at a slightly lower frequency than those
of the other complexes (Table 2). At this time, we cannot explain
these exceptional observation for the bpy complex, but they could
give an important insight into the different reactivity of the bpy
complex from the others [25].
4. Conclusion
In this study, the crystal structures of five (azido)iridium(III)
complexes bearing potentially bidentate ligands (L–L0) have been
determined and their structural parameters have been discussed,
together with those of the related complexes analyzed previously.
Comparing the parameters of the four-membered chelate ring
Fig. 7. A stacking diagram of the pybim complexes in the crystal.

T. Suzuki et al. / Polyhedron 28 (2009) 2287–2293
2293
(b) J. Du Bois, C.S. Tomooka, J. Hong, M.E. Carreira, Acc. Chem. Res. 30 (1997)
364.
[3] (a) H.C. Kolb, M.G. Finn, K.B. Sharpless, Angew. Chem., Int. Ed. 40 (2001) 2004;
(b) M. Obata, A. Kitamura, A. Mori, C. Kameyama, J.A. Czaplewska, R. Tanaka, I.
Kinoshita, T. Kusumoto, H. Hashimoto, M. Harada, Y. Mikata, T. Funabiki, S.
Yano, Dalton Trans. (2008) 3292;
(c) S. Mukhopadhyay, J. Lasri, M.A.J. Charmier, M.F.C. Guedes da Silva, A.J.L.
Pombeiro, Dalton Trans. (2007) 5297.
[4] (a) H.-B. Xu, B.-W. Wang, F. Pan, Z.-M. Wang, S. Gao, Angew. Chem., Int. Ed. 46
(2007) 7388;
formed by Ph2Ppy (in complex 2) with those of the five-membered
chelate ring of the related phosphine–imine-type hybrid ligand
Ph2Pqn (in complex 4), it became apparent that the Ph2Ppy ring
was highly strained as indicated by the smaller bond angles, but
the Ir–P/N coordination bond lengths were comparable to those
in the strain-free Ph2Pqn chelate ring. Although the Ir–N bond
and the Ir–N–C angle in the Ph2Ppy complex 2 are similar to those
in the 2-Spy and 2-Sqn complexes analyzed previously [6,22], com-
plex 2 exhibits a dissociation equilibrium of the Ir–N(py) bond in
acetonitrile solution.
(b) T.-F. Liu, D. Fu, S. Gao, Y.-Z. Zhang, H.-L. Sun, G. Su, Y.-J. Liu, J. Am. Chem.
Soc. 125 (2003) 13976;
(c) J. Carranza, C. Brennan, J. Sletten, J.M. Clemente-Juan, F. Lloret, M. Julve,
Inorg. Chem. 43 (2003) 8716;
The pybim complex showed an interesting molecular and crys-
(d) M. Habib, T.K. Marmakar, G. Aromi, J. Ribas-Ariño, H.-K. Fun, S.
Chantrapromma, S.K. Chandra, Inorg. Chem. 47 (2008) 4109.
[5] T. Suzuki, A.G. Dipasquale, J.M. Mayer, J. Am. Chem. Soc. 125 (2003) 10514.
[6] Y. Sekioka, S. Kaizaki, J.M. Mayer, T. Suzuki, Inorg. Chem. 44 (2006) 8173.
[7] M. Kotera, Y. Sekioka, T. Suzuki, Inorg. Chim. Acta 361 (2008) 1479.
[8] (a) V. Pons, D.M. Heinekey, J. Am. Chem. Soc. 125 (2003) 8428;
(b) K.-I. Fujita, M. Nakamura, R. Yamaguchi, Organometallics 20 (2001) 100.
[9] K. Pachhunga, B. Therrien, K.A. Kreisel, G.P.A. Yap, M.R. Kollipara, Polyhedron
26 (2007) 3638.
tal structure. The ligand, pybimꢁ, forms a planar five-membered
chelate ring with an extended p-delocalized system, and the pybim
plane shows a stacking interaction with the neighboring pybim
and Cp* planes to give a characteristic packing structure of the
crystal. Furthermore, the Ir–N(bim) bond is shorter than the Ir–
N(py) bond, because of the stronger electron-donating properties
of the benzimidazole moiety.
We have also examined the photochemical and thermal reactiv-
ities of the complexes described in this study, but they showed a
complicated mixture of unidentified products.
[10] M. Albrecht, T. Scheiring, T. Sixt, W. Kaim, J. Organomet. Chem. 596 (2000) 84.
[11] K. Yamanari, R. Ito, S. Yamamoto, T. Konno, A. Fuyuhiro, M. Kobayashi, R.
Arakawa, Dalton Trans. (2003) 380.
[12] T. Suzuki, Inorg. Chim. Acta 359 (2006) 2431.
[13] T. Suzuki, Acta Crystallogr., Sect. E 61 (2005) m488.
[14] A. Maisonnet, J.P. Farr, M.M. Olmstead, C.T. Hunt, A.L. Balch, Inorg. Chem. 21
(1982) 3961.
Supplementary data
[15] R.D. Feltham, H.G. Metzer, J. Organomet. Chem. 33 (1971) 347.
[16] (a) PROCESS-AUTO
, Automatic Data Acquisition and Processing Package for
CCDC 711474, 711475, 711476, 711477, and 711478 contain
the supplementary crystallographic data for 1, 2, 3, 4ꢀCH3OH, and
5, respectively. These data can be obtained free of charge via
http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the
Cambridge Crystallographic Data Centre, 12 Union Road, Cam-
bridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail:
deposit@ccdc.cam.ac.uk.
Imaging Plate Diffractometer, Rigaku Corporation, Akishima, Tokyo, Japan,
1998.;
(b) T. Higashi, SHAPE, Program to obtain Crystal Shape using CCD Camera,
Rigaku Corporation, Tokyo, Japan, 1999.;
(c) CRYSTAL STRUCTURE Ver. 3.6.0, Crystal Structure Analysis Package, Rigaku and
Rigaku/MSC, Akishima, Tokyo, Japan and The Woodlands, TX, USA, 2000–2004.
[17] (a) M.C. Burla, R. Caliandro, M. Camalli, B. Carrozzini, G.L. Cascarano, L. De
Caro, C. Giacovazzo, G. Polidori, R. Spagna, SIR2004, 2005.;
(b) G.M. Sheldrich, SHELXL97, University of Göttingen, Göttingen, Germany,
1997.
[18] P. Covindaswamy, P. Carroll, Y.A. Mozharivskyj, M.R. Kollipara, J. Chem. Sci.
118 (2006) 319.
Acknowledgement
[19] M. Kotera, Y. Sekioka, T. Suzuki, Inorg. Chem. 47 (2008) 3498.
[20] M. Rashidi, K. Kamali, M.C. Jennings, R.J. Puddephatt, J. Organomet. Chem. 690
(2005) 1600.
[21] T. Suzuki, T. Kuchiyama, S. Kishi, S. Kaizaki, M. Kato, Bull. Chem. Soc. Jpn. 75
(2002) 2433.
This work was supported by Grant-in-Aid for Scientific
Research No. 20550064 from the Ministry of Education, Culture,
Sports, Science, and Technology, Japan.
[22] Y. Sekioka, T. Suzuki, Bull. Chem. Soc. Jpn. 79 (2006) 1897.
[23] D.A. Freedman, K.R. Mann, Inorg. Chem. 30 (1991) 836.
[24] N.W. Alcock, P.G. Pringle, P. Bergamini, S. Sostero, O. Traverso, J. Chem. Soc.,
Dalton Trans. (1990) 1553.
References
[25] T. Suzuki, Bull. Chem. Soc. Jpn. 77 (2004) 1869.
[26] S. Ye, W. Kaim, M. Albrecht, F. Lissner, T. Schleid, Inorg. Chim. Acta 357 (2004)
3325.
[1] J. Šima, Coord. Chem. Rev. 250 (2006) 2325.
[2] (a) J.F. Berry, E. Bill, E. Bothe, S.D. George, B. Mienert, F. Neese, K. Wieghardt,
Science 312 (2006) 1937;